Offshore oil wells are typically drilled from offshore platforms anchored to the sea floor. Many wells produce oil or oil/water mixtures from an underground formation or reservoir without the need for pumping. Although the produced crude oil may be transferred from the offshore platform to tankers, a transfer pipeline is more commonly provided for moving the liquids to other platforms or shore facilities, e.g., for upgrading or refining. The export pipeline may directly transfer the oil to the shore facilities, or the produced oil may be transferred first to another platform, called an import platform, and then to the shore facilities from the import platform.
The transport pipeline normally comprises an export riser portion (e.g., extending from the outlet of the process equipment down towards the sea floor) and a transfer portion. The transfer portion typically extends along the sea floor from the lower end of the export riser to facilities on-shore or to an oil-importing platform. If the transport pipeline communicates to an importing platform, the pipeline also comprises an import riser extending from the transfer portion end up to the collection apparatus on the import platform.
Because the produced crude oil is frequently viscous and transfer distances may be long, transfer friction losses in the transfer pipeline (and associated backpressure) can be quite high. This increase in backpressure can inhibit the production performance of the well or require large and costly-to-operate transfer pumps. In addition, variable crude oil composition, temperature, and flowrates can also result in crude oil transfers over a wide range of supply, pipeline and outlet conditions, e.g. pressure and flowrate.